C 钩子(Hook)/回调系统

Question

我一直在努力弄清楚如何在 C 中实现 Hook 系统。谁能给我一些指示或示例？

Answer 1

使用函数指针:

struct callbacks {
    void (*somethingHappened)(void *context);
    bool (*shouldIDoSomething)(void *context);
};

void doSomethingAwesome(void *operationData, struct callbacks callbacks)
{
     // context is the data you pass to the function
     if (callbacks.shouldIDoSomething(context))
     {
          // do something
          callbacks.somethingHappened(context);
     }
}

或者，您可以创建一个调度服务:

struct dictionary
{
    char **keys;
    void **values;        

    int count;
};

struct list
{
    void **values;

    int count;
};

// functions to add, remove, etc;

struct dictionary *callbacks = NULL;
void registerForDispatch(char *key, void (*callback)(void *))
{
    if (!callbacks)
    {
        callbacks = dictionary_create(10); // dictionary with 10 key / value pairs
    }

    if (!dictionary_containsKey(callbacks, key))
    {
        struct list *callBacksForKey = list_create(10); // default 10 callbacks, array should be auto-expanding

        dictionary_setValue(callbacks, key, arr);
    }

    struct list *callBacksForKey = dictionary_getValue(callbacks, key);

    list_addObject(callBacksForKey, callback);
}

void unregisterFromDispatch(char *key, void (*callback)(void *))
{
    struct list *callBacksForKey = dictionary_getValue(callbacks, key);

    list_removeObject(callback);
}

void sendNotification(char *key, void *context)
{
    struct list *callBacksForKey = dictionary_getValue(callbacks, key);

    for (int i = 0; list->count; i++)
    {
         void (*callback)(void *) = list->values[i];
         callback(context);
    }
}

使用第二种解决方案，您可以获得单个回调的多个监听器的优势。